U.S. patent number 9,570,753 [Application Number 13/591,802] was granted by the patent office on 2017-02-14 for reversible polarity operation and switching method for znbr flow battery when connected to common dc bus.
This patent grant is currently assigned to EnSync, Inc.. The grantee listed for this patent is Nathan Coad, Kevin Dennis, Peter Lex, Jeffrey A. Reichard. Invention is credited to Nathan Coad, Kevin Dennis, Peter Lex, Jeffrey A. Reichard.
United States Patent |
9,570,753 |
Dennis , et al. |
February 14, 2017 |
Reversible polarity operation and switching method for ZnBr flow
battery when connected to common DC bus
Abstract
An improved electrolyte battery is provided that includes a tank
assembly adapted to hold an amount of an anolyte and a catholyte, a
number of cell stacks operably connected to the tank assembly, each
stack formed of a number of flow frames disposed between end caps
and a number of power converters operatively connected to the cell
stacks. The cell stacks are formed with a number of flow frames
each including individual inlets and outlets for anolyte and
catholyte fluids and a separator disposed between flow frames
defining anodic and cathodic half cells between each pair of flow
frames. The power converter is configured to connect the battery
with either forward or reverse polarity to a DC power source, such
as a DC bus. The anodic and cathodic half cells switch as a
function of the polarity by which the battery is connected to the
Dc power source.
Inventors: |
Dennis; Kevin (Waukesha,
WI), Coad; Nathan (Perth, AU), Lex; Peter
(Menomonee Falls, WI), Reichard; Jeffrey A. (Oconomowoc,
WI) |
Applicant: |
Name |
City |
State |
Country |
Type |
Dennis; Kevin
Coad; Nathan
Lex; Peter
Reichard; Jeffrey A. |
Waukesha
Perth
Menomonee Falls
Oconomowoc |
WI
N/A
WI
WI |
US
AU
US
US |
|
|
Assignee: |
EnSync, Inc. (Menomonee Falls,
WI)
|
Family
ID: |
47746829 |
Appl.
No.: |
13/591,802 |
Filed: |
August 22, 2012 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20120326672 A1 |
Dec 27, 2012 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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13185862 |
Jul 19, 2011 |
9093862 |
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12355169 |
Aug 30, 2011 |
8008808 |
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61526146 |
Aug 22, 2011 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M
10/365 (20130101); H01M 10/46 (20130101); H01M
8/0226 (20130101); H02J 7/34 (20130101); H02J
1/10 (20130101); H01M 12/085 (20130101); H01M
4/0471 (20130101); H01M 4/668 (20130101); H01M
4/96 (20130101); H01M 8/0213 (20130101); H01M
8/0221 (20130101); H01M 4/8875 (20130101); H01M
8/188 (20130101); Y02E 60/10 (20130101); Y02E
60/50 (20130101) |
Current International
Class: |
H02J
7/00 (20060101); H01M 10/46 (20060101); H01M
8/02 (20160101); H01M 12/08 (20060101); H01M
4/96 (20060101); H01M 10/36 (20100101); H01M
4/04 (20060101); H01M 4/66 (20060101); H02J
1/10 (20060101); H02J 7/34 (20060101); H01M
4/88 (20060101); H01M 8/18 (20060101) |
Field of
Search: |
;320/131,135,127,136 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0015096 |
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Sep 1980 |
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EP |
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2002219464 |
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Aug 2002 |
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JP |
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Other References
International Search Report and the Written Opinion of the
International Searching Authority, or the Declaration;
International Application No. PCT/US2012/051860, mailed Jan. 21,
2013--(9 pages). cited by applicant.
|
Primary Examiner: Rodas; Richard Isla
Assistant Examiner: Ruiz; Johali Torres
Attorney, Agent or Firm: Boyle Fredrickson, SC
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims priority to U.S. provisional application
Ser. No. 61/526,146, filed Aug. 22, 2011 and entitled Power Systems
Formed with Cell Stacks Including a Number of Flowing Electrolyte
Batteries and Methods of Operation. This application is also a
continuation-in-part of U.S. patent application Ser. No.
13/185,862, filed Jul. 19, 2011 now U.S. Pat. No. 9,093,862 and
entitled Method and Apparatus for Controlling a Hybrid Power
System, which is, in turn, a continuation-in-part of U.S. patent
application Ser. No. 12/355,169, filed Jan. 16, 2009, entitled
Method and Apparatus for Controlling a Hybrid Power System, which
issued as U.S. Pat. No. 8,008,808 on Aug. 30, 2011. The entire
contents of each of the afore-mentioned applications are
incorporated herein by reference.
Claims
We claim:
1. A method of controlling the level of charge on a battery
connected to a DC bus via a power converter, comprising the steps
of: receiving a command at the power converter to begin discharging
the battery; regulating current flow from the battery to the DC bus
at a first amplitude by generating a plurality of switching signals
within the power converter to control a plurality of switching
devices located within the power converter to selectively connect
the battery to the DC bus; monitoring an amplitude of voltage
present on the battery; increasing the frequency at which the
switching signals are generated when the amplitude of voltage
present on the battery reaches a first threshold; regulating
current flow from the battery to the DC bus at a second amplitude
when the amplitude of voltage present on the battery reaches the
first threshold; latching on at least one of the switching devices
when the amplitude of voltage present on the battery reaches a
second threshold; and disabling the discharging of the battery when
the amplitude of voltage present on the battery is substantially
zero.
2. The method of claim 1 wherein regulating current flow between
the battery and the DC bus at a first amplitude is performed with a
first polarity of voltage on the battery and wherein after
disabling the discharging of the battery, the method further
comprises the step of regulating current flow between the battery
and the DC bus by generating a plurality of switching signals
within the power converter to control the plurality of switching
devices to selectively connect the battery to the DC bus according
to a second polarity, where the second polarity is opposite the
first polarity.
3. The method of claim 1 wherein the frequency at which the
switching signals are generated is a function of one of the voltage
present and the desired power losses at the battery.
4. A method of controlling the level of charge on a battery
connected to a DC bus via a power converter, comprising the steps
of: receiving a command at the power converter to begin discharging
the battery; regulating current flow between the battery and the DC
bus by generating a plurality of switching signals within the power
converter to control a plurality of switching devices located
within the power converter to selectively connect the battery to
the DC bus according to a first polarity; monitoring the amplitude
of voltage present on the battery; regulating current flow from the
battery to the DC bus at a first amplitude; increasing the
frequency at which the switching signals are generated when the
amplitude of voltage present on the battery reaches a first
threshold; regulating current flow from the battery to the DC bus
at a second amplitude when the amplitude of voltage present on the
battery reaches the first threshold; and latching on at least one
of the switching devices when the amplitude of voltage present on
the battery reaches a second threshold; disabling the discharging
of the battery when the amplitude of voltage present on the battery
is substantially zero; and regulating current flow between the
battery and the DC bus by generating a plurality of switching
signals within the power converter to control the plurality of
switching devices to selectively connect the battery to the DC bus
according to a second polarity, where the second polarity is
opposite the first polarity.
5. The method of claim 4 wherein the frequency at which the
switching signals are generated is a function of one of the voltage
present and the desired power losses at the battery.
Description
BACKGROUND OF THE INVENTION
The present invention relates generally to power supply systems,
and more specifically to power supply systems including flowing
electrolyte batteries.
Batteries used in certain prior art stand alone power supply
systems are commonly lead-acid batteries. However, lead-acid
batteries have limitations in terms of performance and
environmental safety. Typical lead-acid batteries often have very
short lifetimes in hot climate conditions, especially when they are
occasionally fully discharged. Lead-acid batteries are also
environmentally hazardous, since lead is a major component of
lead-acid batteries and can cause serious environmental problems
during manufacturing and disposal.
Flowing electrolyte batteries, such as zinc-bromine batteries,
zinc-chlorine batteries, and vanadium flow batteries, offer a
potential to overcome the above mentioned limitations of lead-acid
batteries. In particular, the useful lifetime of flowing
electrolyte batteries is not affected by deep discharge
applications, and the energy to weight ratio of flowing electrolyte
batteries is up to six times higher than that of lead-acid
batteries.
However, manufacturing flowing electrolyte batteries can be more
difficult than manufacturing lead-acid batteries. A flowing
electrolyte battery, like a lead acid battery, comprises a stack of
cells to produce a certain voltage higher than that of individual
cells. But unlike a lead acid battery, cells in a flowing
electrolyte battery are hydraulically connected through an
electrolyte circulation path. This can be problematic as shunt
currents can flow through the electrolyte circulation path from one
series-connected cell to another causing energy losses and
imbalances in the individual charge states of the cells. To prevent
or reduce such shunt currents, flowing electrolyte batteries
require sufficiently long electrolyte circulation paths between
cells, thereby increasing electrical resistance between cells.
Another problem of flowing electrolyte batteries is a need for a
uniform electrolyte flow rate in each cell in order to supply
chemicals evenly inside the cells. To achieve a uniform flow rate
through the cells, flowing electrolyte batteries define complex
flow distribution zones. However, because electrolyte often has an
oily, aqueous and gaseous multiphase nature, and because of
structural constraints on the cells, uniform flow rates are often
not achieved.
Another issue in these types of batteries where the battery employs
an array of stacks of cells is that the stacks share a common
flowing electrolyte. Since the stacks share the electrolyte,
measurements of the open-circuit voltage across a stack only
indicate whether the stack stores some non-zero amount of charge,
rather than indicating the stack's state of charge relative to the
other stacks in the system. Moreover, differences in the open
circuit voltages between stacks are typically indicative of some
internal abnormality that has altered a stack's internal
resistance.
For example, in a zinc-bromine flowing electrolyte battery, the
stacks share an aqueous zinc bromide electrolyte and have their own
electrodes for deposit and dissolution of elemental zinc during
charge and discharge cycles. In this type of battery, the
electrolyte flow to a stack can be inhibited by poorly placed zinc
deposits. Additionally, nucleation on the electrodes can cause
dendrite formation and branching between cells. In either case, the
internal resistance of the affected stack or the open-circuit
voltage across the stack could be lowered.
Differences in open-circuit voltages between parallel-connected
stacks in flowing electrolyte battery systems can affect the charge
and discharge cycles of the stacks and, potentially, the operation
of the battery. For example, in the aforementioned zinc-bromine
battery, a lowered open circuit voltage in a particular stack
causes an increase in the rate of zinc accumulation in the faulty
stack during the charge cycle and a decrease in the rate of zinc
reduction in the faulty stack during the discharge cycle. Moreover,
the additional zinc stored in the faulty stack typically comes from
the electrolyte normally utilized by neighboring stacks. As a
result of the lowered zinc availability, the energy storage
capacity of the neighboring stacks may be reduced. Another
consequence is that the stack having the increased zinc
accumulation does not fully deplete the zinc during discharge;
eventually resulting in zinc accumulating on the electrodes of the
faulty stack to such an extent that it causes internal short
circuiting between the cells of the stack. This can potentially
destroy the stack and possibly, the entire battery system. A
further consequence is that the increased zinc accumulation can
restrict the channels through which the electrolyte flows. As the
electrolyte flow acts to cool the stack, the restricted flow may
cause the stack to overheat.
In order to restore open-circuit voltages to a more uniform value,
an equalization process may be executed. The equalization process
includes fully "stripping", i.e., fully discharging, each stack in
the battery, completely removing any stored charge from all of the
cells in all of the stacks. Ideally, this process eliminates the
abnormality that initially caused the difference in open-circuit
voltage between the stacks. For example, a full strip typically
dissolves dendrites between plates and/or deposits obstructing
electrolyte flow. However, a full strip of each of the cell stacks
in the battery typically renders the battery entirely unavailable
or available at a significantly reduced capacity for electrical
applications, necessitating the purchase and installation of
additional redundant battery systems. Moreover, a full strip is
often unnecessary since typically a minority of the stacks in the
battery is operating abnormally.
In addition, existing methods of stripping battery stacks in a
flowing electrolyte battery are typically time consuming and may
have to be repeated every few days for a recurring problem. When
stripping, i.e., fully discharging, a cell stack, care must be
taken to avoid cell reversal in which the polarity of one of the
stacks becomes opposite the polarity of the other stacks. In such
an instance, the cell stack with the reversed polarity becomes a
load, drawing current from the other stacks. Thus, during
discharge, a cell stack is first discharged to a low voltage level
using a higher current. When the stack reaches the low voltage
level, the magnitude of the current is reduced to slow the rate of
discharge. As the voltage level continues to drop, the magnitude of
current is repeatedly stepped down to reduce the rate of discharge
as the voltage level approaches zero. By approaching the zero
voltage level at a slow rate, discharge of the cell stack is
discontinued when zero voltage is reached. While this stepped
reduction in the discharge current avoids cell reversal, it is also
a significant factor in the time required to strip the cell stacks
in a battery.
Therefore, there is a need for an improved electrolyte flow battery
design and methods and apparatus for controlling, monitoring,
charging and/or discharging cells in a flowing electrolyte
battery.
BRIEF DESCRIPTION OF THE INVENTION
Various aspects of the present invention have been developed to
overcome or alleviate one or more limitations of the prior art
including providing improved structures of the cell stack and the
individual cells to reduce manufacturing costs and to improve the
structure of a cell stack for a flowing electrolyte battery and
providing improved control of power flow between the battery and a
common bus to which it is connected to reduce the amount of time
required to equalize individual stacks in a battery system.
Thus, according to one aspect of the present invention, the
invention provides an improved cell stack including modular battery
cells to reduce manufacturing costs and to improve the structure
and implementation and operation of a cell stack for a flowing
electrolyte battery.
According to another aspect of the present invention, the invention
addresses the deficiencies in the prior art by providing, in
various embodiments, improved methods, systems and features for
controlling, monitoring, charging and/or discharging (collectively
"controlling") flowing electrolyte batteries. According to one
aspect, the invention addresses the deficiencies in the prior art
by providing methods, systems and features for controlling
individual stacks of battery cells in a flowing electrolyte
battery. In a further embodiment, the invention provides methods,
systems and features for controlling individual battery stacks in a
flowing electrolyte battery. Among other advantages, the invention
increases the flexibility with which cell stacks can be charged and
stripped; enables regular and ongoing battery maintenance, without
taking the battery offline; maintains the battery at a predictable
and consistent charge capacity; reduces the likelihood of stack
failures due, for example, to electrolyte flow blockage, thermal
runaway, and/or dendrite formation; reduces the risk of uneven cell
plating; increases the number of charge/discharge cycles available;
and reduces expenses relating to maintaining redundant battery
systems.
According to yet another aspect of the present invention, an
improved electrolyte battery is provided that includes a tank
assembly adapted to hold an amount of an anolyte and a catholyte, a
number of cell stacks operatively connected to the tank assembly,
each stack formed of a number of flow frames disposed between end
caps and a number of power converters operatively connected to the
cell stacks. The cell stacks are formed with a number of flow
frames each including individual inlets and outlets for anolyte and
catholyte fluids and a separator disposed between flow frames
defining anodic and cathodic half cells between each pair of flow
frames. The power converter is configured to connect the battery
with either forward or reverse polarity to a DC power source, such
as a DC bus. The anodic and cathodic half cells switch as a
function of the polarity by which the battery is connected to the
DC power source.
According to one embodiment of the invention, a power converter for
regulating current flow between a DC bus and an energy storage
device includes a first set of terminals configured to be connected
to the DC bus and a second set of terminals configured to be
connected to the energy storage device. The first set of terminals
has a first electrical polarity and the second set of terminals has
a second polarity. A plurality of switches selectively connects the
first set of terminals to the second set of terminals. A memory
device stores a plurality of instructions, and a processor is
configured to execute the plurality of instructions for operation
in a first operating mode and a second operating mode. During the
first operating mode, the first electrical polarity and the second
electrical polarity are the same, and during the second operating
mode, the first electrical polarity and the second electrical
polarity are reversed.
According to another aspect of the invention, the plurality of
switches may further include a first set of switches configured to
regulate current flow between the DC bus and the energy storage
device and a second set of switches configured to select one of the
first operating mode and the second operating mode. The energy
storage device may be a flow battery having at least one cell
stack. The power converter then regulates the current flow between
the DC bus and either one cell stack of the flow battery or a
plurality of cell stacks of the flow battery.
According to another embodiment of the invention, a method of
controlling the level of charge on a battery connected to a DC bus
via a power converter includes the steps of receiving a command at
the power converter to begin discharging the battery, regulating
current flow between the battery and the DC bus at a first
amplitude by generating a plurality of switching signals within the
power converter to control a plurality of switches to selectively
connect the battery to the DC bus, and monitoring the amplitude of
voltage present on the battery. The frequency at which the
switching signals are generated is increased and the current flow
is regulated at a second amplitude between the battery and the DC
bus when the amplitude of voltage present on the battery reaches a
first threshold. At least one of the switches is latched on when
the amplitude of voltage present on the battery reaches a second
threshold, and discharging of the battery is disabled when the
amplitude of voltage present on the battery is substantially
zero.
According to another aspect of the invention, regulating current
flow between the battery and the DC bus at a first amplitude is
performed with a first polarity of voltage on the battery. After
discharging of the battery is disabled, the method further includes
the step of regulating current flow between the battery and the DC
bus by generating a plurality of switching signals within the power
converter to control a plurality of switches to selectively connect
the battery to the DC bus according to a second polarity, where the
second polarity is opposite the first polarity.
According to still another embodiment of the invention, a method of
controlling the level of charge on a battery connected to a DC bus
via a power converter includes the steps of receiving a command at
the power converter to begin discharging the battery, regulating
current flow between the battery and the DC bus by generating a
plurality of switching signals within the power converter to
control a plurality of switches to selectively connect the battery
to the DC bus according to a first polarity, and monitoring the
amplitude of voltage present on the battery. Discharging of the
battery is disabled when the amplitude of voltage present on the
battery is substantially zero, and current flow between the battery
and the DC bus is regulated by generating a plurality of switching
signals within the power converter to control a plurality of
switches to selectively connect the battery to the DC bus according
to a second polarity, where the second polarity is opposite the
first polarity.
According to yet another aspect of the invention and after the step
of monitoring the amplitude of voltage present on the battery, the
method further includes the steps of regulating current flow
between the battery and the DC bus at a first amplitude, increasing
the frequency at which the switching signals are generated when the
amplitude of voltage present on the battery reaches a first
threshold, regulating current flow between the battery and the DC
bus at a second amplitude when the amplitude of voltage present on
the battery reaches the first threshold, and latching on at least
one of the switches when the amplitude of voltage present on the
battery reaches a second threshold.
These and other objects, advantages, and features of the invention
will become apparent to those skilled in the art from the detailed
description and the accompanying drawings. It should be understood,
however, that the detailed description and accompanying drawings,
while indicating preferred embodiments of the present invention,
are given by way of illustration and not of limitation. Many
changes and modifications may be made within the scope of the
present invention without departing from the spirit thereof, and
the invention includes all such modifications.
BRIEF DESCRIPTION OF THE DRAWING(S)
Various exemplary embodiments of the subject matter disclosed
herein are illustrated in the accompanying drawings in which like
reference numerals represent like parts throughout, and in
which:
FIG. 1 is an isometric view of the battery module constructed
according to the present disclosure;
FIG. 2 is a front plan view of the module of FIG. 1;
FIG. 3 is a partial front plan front view of the module of FIG.
1;
FIG. 4 is an exploded, isometric view of the module of FIG. 3;
FIG. 5 is an isometric view of the anolyte flow system of the
module of FIG. 1;
FIG. 6 is an exploded, isometric view of the flow system of FIG.
5;
FIG. 7 is a front plan view of the flow system of FIG. 5;
FIG. 8 is a side plan view of the flow system of FIG. 5;
FIG. 9 is a top plan view of the flow system of FIG. 5;
FIG. 10 is an exploded, isometric view of a catholyte flow system
of the module of FIG. 1;
FIG. 11 is a front plan view of the flow system of FIG. 10;
FIG. 12 is a side plan view of the flow system of FIG. 10;
FIG. 13 is a top plan view of the flow system of FIG. 10;
FIG. 14 is a partial exploded, isometric view of the module of FIG.
1;
FIG. 15 is a front plan view of the module of FIG. 14;
FIG. 16 is a top plan view of the module of FIG. 14;
FIG. 17 is a right side plan view of the module of FIG. 14;
FIG. 18 is a partial exploded, isometric view of the module of FIG.
1;
FIG. 19 is a front plan view of the module of FIG. 18;
FIG. 20 is a top plan view of the module of FIG. 18;
FIG. 21 is a right side plan view of the module of FIG. 18;
FIG. 22 is an isometric view of a cell stack for use in the module
of FIG. 1;
FIG. 23 is a front plan view of a flow frame employed in the cell
stack of FIG. 22;
FIG. 24 is a front plan view of an end cap of the cell stack of
FIG. 22;
FIG. 25 is a rear plan view of a the end cap of FIG. 24;
FIG. 26 is a partially broken away front plan view of a first
embodiment of a spacer material utilized in the cell stack of FIG.
22;
FIG. 27 is a partially broken away front plan view of a second
embodiment of the spacer material of FIG. 26;
FIG. 27A is a partially broken away front plan view of the spacer
material of FIG. 27;
FIG. 28 is a graphical representation of the measurement of the
state of charge of the module of FIG. 1;
FIG. 29 is a schematic representation of one embodiment of a DC/DC
converter for use in the module of FIG. 1;
FIG. 30 is a block diagram representation of a first operating mode
of the DC/DC converter of FIG. 29;
FIG. 31 is a block diagram representation of a second operating
mode of the DC/DC converter of FIG. 29;
FIG. 32 is a block diagram representation of a third operating mode
of the DC/DC converter of FIG. 29;
FIG. 33 is a block diagram representation of a fourth operating
mode of the DC/DC converter of FIG. 29;
FIG. 34 is a flowchart illustrating operation of the DC/DC
converter of FIG. 29;
FIG. 35 is a flowchart illustrating the discharge step of the
flowchart of FIG. 34; and
FIG. 36 is a flowchart illustrating the high loss switching
operation for the flowchart of FIG. 34.
In describing the preferred embodiments of the invention which are
illustrated in the drawings, specific terminology will be resorted
to for the sake of clarity. However, it is not intended that the
invention be limited to the specific terms so selected and it is
understood that each specific term includes all technical
equivalents which operate in a similar manner to accomplish a
similar purpose. For example, the word "connected," "attached," or
terms similar thereto are often used. They are not limited to
direct connection but include connection through other elements
where such connection is recognized as being equivalent by those
skilled in the art.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
With reference now to the drawing figures in which like reference
numerals designate like parts throughout the disclosure, the
electrolyte battery module and system according to one embodiment
of the present invention is illustrated generally at 10 in FIGS.
1-4 and 14-21. The battery system 10 includes as general components
a cabinet 12, an assembly of cell stacks 14 positioned within the
cabinet 12, a tank assembly 16 positioned within the cabinet 12.
The tank assembly 16 includes an anolyte flow system 18 (FIGS. 5-9)
and and a catholyte flow system 20 (FIGS. 10-13) each having a pump
19 and suitable piping 21 operably connected to the cell stacks 14.
The anolyte is the portion of the electrolyte in proximity to the
anode, or negative cell, in the battery, and, the catholyte is the
portion of the electrolyte in proximity to the cathode, or positive
cell, in the battery. In a discharged state, the electrolyte in
each system 18, 20 is substantially identical. As the cell stacks
14 are charged, the electrolyte in the anolyte flow system 18
becomes negatively charged and the electrolyte in the catholyte
flow system becomes positively charged. As will be discussed in
detail below, the battery system 10 is configured such that the
polarity of the cell stacks 14 may be reversed. Consequently, each
of the flow systems, 18 and 20, are interchangeable as the anolyte
or catholyte flow system as a function of the polarity of the cell
stacks 14.
A DC/DC converter housing 22 located within the cabinet 12 includes
one or more DC/DC converters 24 that are operably connected to the
cell stacks 14. A bus bar 28 is operatively connected to the DC/DC
converters 24 and power may be passed bi-directionally between the
cell stacks 14 and the bus bar 28 via the DC/DC converters 24. A
heat exchanger 26 is disposed within the cabinet 12, and fans (not
shown) may be affixed to fan mounts 27 on the cabinet 12. The
battery system 10 also includes a controller 100 operatively
connected to various components of the battery system 10, including
the pumps 19 and the converters 24, among others.
Looking at FIGS. 5-9 the anolyte flow system 18 has a pump 19,
piping 21, and a three way valve 30. Piping 21 leads from the
portion of the tank assembly 16 in which the anolyte is held to the
pump 19 for distribution of the anolyte to the cell stacks 14. The
anolyte returns from the cell stacks 14 to the tank assembly 16
through additional piping 21 and can be diverted through the heat
exchanger 26 by operation of the three way valve 30.
Referring now to FIGS. 10-13, the catholyte flow system 20 is
formed similarly to the anolyte flow system 18 and also has a pump
19, piping 21, and a four way valve 32. Piping 21 leads from the
portion of the tank assembly 16 in which the catholyte is held to
the pump 19 for distribution of the catholyte to the cell stacks
14. The catholyte returns from the cell stacks 14 returns to the
tank assembly 16 through additional piping 21 and flow direction
through the stacks can be reversed by operation of the four way
valve 32.
Referring next to FIGS. 22-25, the cell stack 14 is illustrated.
The cell stack 14 is formed of a number of flow frames 34 disposed
between a pair of end caps 36. Each of the flow frames 34 is molded
to include half of the flow paths and other features on each side
of the flow frame 34. A separator is included between each pair of
flow frames 34 and adjacent flow frames 34 and separators are
joined, for example by ultrasonic welding, vibration welding, or
any other suitable joining method, to define flow paths between the
flow frames 34. Each end cap 36 is molded to include the flow paths
on one side of the end cap 36, which is oriented inward to the cell
stack 14 such that the end cap 36 and the adjacent flow frame 34
similarly define a flow path. The other side of the end cap 36 is
molded to include structural features of the cell stack 14 and to
facility joining cell stacks 14 to each other.
With reference then to one side of each flow frame 34 and the
internal facing sides of each end cap 36, the following features
are molded into flow frames 34 and end caps 36. For reference, the
features will be discussed with respect to one side of a flow frame
34, but are similarly applicable to both sides of the flow frame 34
and one side of the end cap 36. A flow frame 34 includes an upper
edge 62, a lower edge 64, and a pair of side edges 66 extending
between the upper and lower edges, 62 and 64 respectively. An
opening 37 proximate to each of the corners of the flow frame 34
provides either an inlet/outlet for electrolyte entering/exiting
the cell stack 14 or a fluid passage to conduct electrolyte between
flow frames 34.
According to one embodiment of the invention, one of the openings
37 proximate to either the upper edge 62 or the lower edge 64
provides a fluid inlet and one of the openings 37 proximate to the
opposite edge, 62 or 64, provides a fluid outlet for electrolyte
passing over the electrode contained between each flow frame 34 and
separator. The other opening 37 proximate to each of the upper and
lower edges 62, 64 defines a channel allowing electrolyte to pass
through a flow frame 34 or separator, but not be directed over the
electrode contained therebetween. The openings 37 are configured
such that electrolyte in the anolyte flow system 18 is directed
down one side of the flow frame 34 and electrolyte in the catholyte
flow system 20 is directed down the other side of the flow frame
34. The separator isolates the anolyte and the catholyte between
adjacent flow frames 34. However, ion transfer may occur across the
separator allowing current to flow in the cell stack 14. In this
manner, the electrolyte flowing through the cell stack is divided
into two flow paths to pass over electrodes on alternating sides of
flow frames 34.
An internal header system 38 is defined proximate to each of the
upper and lower edges, 62 and 64 respectively, to define flow
channels for electrolyte distribution between flow frames 34. The
internal header system 38 receives electrolyte from either the
anolyte flow system 18 or the catholyte flow system and guides it
through a first channel generally across the width of the flow
frame 34 proximate to the upper edge 62. The internal header system
38 then guides the electrolyte through a return channel to a
central portion of the flow frame 34. The electrolyte is
subsequently divided into multiple flow paths at generally even
spacing between each side 66 of the flow frame 34 to form flow
channels for distribution of the electrolyte of the electrode. The
internal header system 38 further includes an integrated filter 39
proximate to each of the inlet and outlet openings 37 to prevent
large particles from entering and potentially blocking the flow
paths in the header system 38. Mixing chevrons 41 are included in
the flow channels to mix the multi-phase electrolyte into a
continuous emulsion as it flows through the flow frame 34. The
internal header system 38 both increases the electrolyte flow path,
thereby increasing the internal resistance and reducing shunt
currents flowing through the cell stack 14, and creates a more
uniform distribution of electrolyte between flow frames 34.
According to the illustrated embodiment, the flow frame 34 further
includes features used to join flow frames and separators to form a
cell stack 14. Vibration weld beads 40 are molded into each flow
frame 34. The vibration weld beads 40 are used to join flow frames
34 to assemble the cell stack 14 and to maintain rigidity of the
cell stack 14 under pressure. The flow frames 34 also include flash
traps to contain the flash generated during the vibration welding
process. The flow frame or separator frame is made of insert or
over molding materials and incorporates pins around the perimeter
of the inserted part to push the insert to one side. This allows
the complete flow frame 34 or separator frame to be completely
assembled in the mold, eliminating many manual assembly operations.
Welding alignment features 38, include, but are not limited to, the
displayed pins and pin holes. Built-in visual inspection features
ensure proper assembly, both prior to and following stack
assembly.
Referring to FIGS. 23 and 24, the internal side of each end cap 36
is of similar construction to one side of the flow frame 34. The
end cap 36 includes an internal header system 47 having an
integrated filter 48 and mixing chevrons 50. The end cap 36 further
includes construction elements such as the vibration weld beads 49,
and built-in visual inspection features 53 to ensure proper
assembly. The end caps 36 further include an o-ring groove on one
corner and a solid surface on the opposite corner for sealing one
stack to another. The end cap may be inserted or overmolded around
the terminal electrode 55 for in mold assembly and a hermetically
sealed battery stack 14, including materials and molding method
incorporating pins around the perimeter of the inserted part to
push the insert to one side
The zinc bromine battery uses a spacer mesh material in each
electrolyte half cell to maintain a constant cell gap thickness and
to prevent the electrode and separator membrane from coming in
contact with each other. The spacer needs to provide dimensional
stability without preventing electrolyte flow through the flow
channels.
In one embodiment shown in FIG. 26, the spacer design used a
biaxially oriented polypropylene netting which is stretched in both
directions under controlled conditions to produce strong, flexible,
light weight netting.
In a second embodiment shown in FIGS. 27 and 27A, extruded netting
produced in a diamond (bi-planar) configuration provides improved
battery performance. Flow tests showed improved distribution of the
bromine electrolyte across the face of the electrode, and battery
performance testing also showed a significant improvement in
current distribution between half stacks which in turn provided
improved energy efficiency.
The battery system 10 uses a bi-planar polypropylene mesh to
improve the consistency of the cell gap and distribution of
electrolyte and Bromine over the active cell area. The mesh
consists of two layers of parallel strands, where the strands in
each layer are disposed at angles with respect to one another,
e.g., are oriented perpendicular to each other. Further, the mesh
can be orientated in the cell so that each layer of strands is at
an angle with respect to the electrolyte flow direction, e.g. at an
angle of 45 degrees to the electrolyte flow direction.
According to one embodiment of the invention, a separate DC/DC
converter 24 individually operates and controls each cell stack 14
in the flow battery system 10. Previous tests have shown that cell
stacks 14 can be operated individually without affecting the
performance of the remaining cell stacks 14. Also, when cell stacks
14 are connected electrically in parallel, the cell stacks 14 will
operate at a common DC voltage, but the current delivered from or
accepted by each cell stack 14 can vary significantly to maintain
the common DC voltage on each stack. Further, by providing separate
DC/DC converters 24 for each cell stack 14, one cell stack 14 may
be stripped while the remaining cell stacks 14 remain operational
in the standard charge/discharge configuration.
According to one embodiment of the invention, the battery system 10
is equipped with eight (8) cell stacks 14 each independently
connected to a DC/DC converter 24. This structure allows the module
10 to optimize energy flow to individual cell stacks 14 using the
DC bus voltage as a set point to charge and discharge. One example
of this structure is illustrated in co-pending U.S. patent
application Ser. No. 13/185,862, incorporated herein by reference
in its entirety. This application discusses a hysteretic control
method by which power is transferred in a bidirectional manner
between the DC bus 28 and each cell stack 14 via the corresponding
DC/DC converter 24. Each DC/DC converter 24 includes separate set
points at which the cell stack 14 is charged or discharged. For
example, stacks with a lower state of charge may have their DC/DC
converters 24 set to charge at a lower DC bus set-point (e.g., 351
V) while stacks with a higher state of charge may have their DC/DC
converters 24 set to charge at a higher DC bus set point (e.g., 355
V). Thus, energy on the DC bus 28 gets stored first in the cell
stacks 14 with a lower state of charge. The set points may
similarly be staggered for discharging cell stacks 14. Cell stacks
14 with a high state of charge may have their DC/DC converters 24
set to discharge at a higher DC bus set point (e.g., 330 V) while
cell stacks 14 with a lower state of charge may have their DC/DC
converters 24 set to discharge at a lower DC bus set point (e.g.,
325 V). Thus, energy is supplied to the DC bus 28 first from the
cell stacks 14 with a higher state of charge. It is further
contemplated that one DC/DC converter 24 may be connected to two or
more cell stacks 14. Multiple cell stacks 14 may be connected in
series, in parallel, or a combination thereof, resulting in an
energy storage device having a desired voltage and energy storage
capacity. The set of cell stacks 14 connected to the DC/DC
converter 24 is controlled in a similar manner as the individual
cell stacks 14 discussed above.
According to another aspect of the invention, the DC/DC converter
24 is configured to operate with either polarity present at the
cell stack 14. In a first operating mode polarity at the cell stack
14 is the same as the polarity at the DC bus 28. In a second
operating mode, the polarity at the cell stack 14 is reversed from
the polarity at the DC bus 28.
Referring next to FIG. 29, an exemplary polarity reversing DC/DC
converter 24 is illustrated. The DC/DC converter includes a
processor 200 in communication with a memory device 202. The
processor 200 may be, but is not limited to, a microprocessor, a
field programmable gate array (FPGA), an application specific
integrated circuit (ASIC), a logic circuit, or any combination
thereof, and may further include one or more of the aforementioned
devices operating in series or in parallel. The memory device 202
may similarly be implemented in a single device or multiple devices
and may include static memory, dynamic memory, or a combination
thereof. The memory device 202 is configured to store, for example,
operating parameters and programs, or a series of instructions
executable by the processor 200. The processor 204 is further in
communication with a gate driver 204. The gate driver 204 may be,
but is not limited to a microprocessor, a field programmable gate
array (FPGA), an application specific integrated circuit (ASIC), a
logic circuit, and may also be integrated into a single device with
the processor 200. The processor 200 receives feedback signals from
sensors corresponding to the amplitude of the voltage and/or
current at various points throughout the DC/DC converter 24. The
locations are dependent on the specific control routines being
executed within the processor 200. For example, DC bus sensors 200
may provide an amplitude of the voltage present on the DC bus 212.
Optionally, a DC bus sensor 200 may be operatively connected to
provide an amplitude of the current conducted on a DC bus 214
internal to the DC/DC converter 24. Similarly a current and/or a
voltage sensor, 250 and 252, may be operatively connected to
provide an amplitude of the current and/or voltage at a cell stack
14 connected to the DC/DC converter 24.
The DC/DC converter 24 further includes a pair of input terminals
210 configured to be connected to the DC bus 28 of the battery
system 10. Each terminal 210 is then connected to the internal DC
bus 212 within the DC/DC converter 24. The internal DC bus 212
includes a positive rail 214 and a negative rail 216. As is
understood in the art, the positive rail 214 and the negative rail
216 may conduct any suitable DC voltage potential with respect to a
common or neutral voltage and are not limited to a positive or a
negative DC voltage potential. Further, either of the positive rail
214 or the negative rail 216 may be connected to a neutral voltage
potential. The positive rail 214 typically conducts a DC voltage
having a greater potential than the negative rail 216. A
capacitance 218 is connected between the positive rail 214 and the
negative rail 216 of the internal DC bus 212. The capacitance 218
may be a single capacitor or any number of capacitors connected in
series or parallel according to the system requirements.
A plurality of switching devices 230, 240 selectively connect the
internal DC bus 212 to the output terminals 260. The switching
devices 230, 240 are typically solid-state power devices,
including, but not limited to, bipolar junction transistors (BJTs),
field effect transistors (FETs), thyristors, or silicon controlled
rectifiers (SCRs). Optionally, the switching devices 230, 240 may
be electro-mechanical devices or any other suitable switching
device configured according to the application requirements. A
diode 232, 242 is connected in parallel to each of the switching
devices 230, 240 for reverse conduction across the switching device
230, 240 as required when the switching device 230, 240 is turned
off. A first set of switching devices 230 is used to control the
polarity of the voltage at the output terminals 260. Each of the
first set of switching devices 230 receives one of the
corresponding first set of gating signals 206. A second set of
switching devices 240 is used to regulate the amplitude and
direction of the current between the internal DC bus 212 and the
output terminals 260. Each of the second set of switching devices
240 receives one of the corresponding second set of gating signals
208. Inductors 246 and 248 are included in series between the
second set of switching devices 240 and the output terminals 260 to
facilitate regulation of the current between the internal DC bus
212 and the output terminals 260.
In operation, the DC/DC converter 24 is configured to regulate
bidirectional current flow between the DC bus 28 and one or more
cell stacks 14 connected to the DC/DC converter 24. The DC/DC
converter 24 is also configured to connect to the cell stack 14 in
either a forward or a reverse polarity with respect to the DC bus
28 and to switch between polarities of the cell stack 14 while
maintaining a constant polarity at the connection to the DC bus 28.
Referring again to FIG. 29, the processor 200 is configured to
execute a series of instructions stored in the memory device 202.
The processor 200 generates reference signals to the gate driver
204 which, in turn, generates gating signals 206, 208 to control
operation of the switching devices 230, 240. Optionally, the gate
driver 204 is integrated in the processor 200 and the processor 200
is further configured to generate the gating signals 206, 208.
According to the illustrated embodiment, the first set of gating
signals 206 control operation of the first set of switching devices
230, and the first set of switching devices 230 is configured to
control the polarity of the voltage at the output terminals 260.
The first set of switching devices 230 are configured such that
only one of transistor one, Q1, or transistor two, Q2, is enabled
at a time. When transistor one, Q1, is enabled, the polarity of the
output terminals 260 is reversed with respect to the polarity of
the DC bus 212. When transistor two, Q2, is enabled, the polarity
of the output terminals 260 is the same as the polarity of the DC
bus 212.
The second set of gating signals 208 control operation of the
second set of switching devices 240, and the second set of
switching devices 240 is configured to control the current between
the DC bus 212 and the output terminals 260. As illustrated, two
pairs of the second set of switching devices 240 are included. The
first pair includes transistor three, Q3, and transistor four, Q4;
and the second pair includes transistor five, Q5, and transistor
six, Q6. Optionally, a single pair of the second set of switching
devices 240 may be included. When transistor one, Q1, is enabled
such that polarity of the output terminals 260 are of opposite
polarity to the DC bus 212, toggling of transistors four and six,
Q4 and Q6 respectively, operate to charge the cell stack 14
connected to the DC/DC converter 24. Conversely, when transistor
one, Q1, is enabled such that polarity of the output terminals 260
are of opposite polarity to the DC bus 212, toggling of transistors
three and five, Q3 and Q5 respectively, operate to discharge the
cell stack 14 connected to the DC/DC converter 24. When transistor
two, Q2, is enabled such that polarity of the output terminals 260
are of the same polarity as the DC bus 212, toggling of transistors
three and five, Q3 and Q5 respectively, operate to charge the cell
stack 14 connected to the DC/DC converter 24. Conversely, when
transistor two, Q2, is enabled such that polarity of the output
terminals 260 are of the same polarity as the DC bus 212, toggling
of transistors four and six, Q4 and Q6 respectively, operate to
discharge the cell stack 14 connected to the DC/DC converter 24. It
is further contemplated the switching devices 230, 240 may be
controlled in varying combinations and according to varying control
routines to control the polarity of the voltage at the output
terminals 260 and to charge/discharge the cell stack 14.
Referring also to FIGS. 30-33, operation of the power converter 24
while charging and discharging with both forward and reverse
voltage polarities present at the battery terminals 55 is
disclosed. During standard operation (i.e. other than equalization
or stripping of a cell stack 14), the processor 204 retrieves the
voltage set points from the memory device 202 at which the DC/DC
converter 24 is to either charge or discharge the cell stack 14.
The DC/DC converter 24 operates according to either FIGS. 30 and 31
or FIGS. 32 and 33 according to the polarity presently commanded at
the battery terminals 55. If a polarity reversal is commanded, the
DC/DC converter 24 fully discharges the cell stack 14, reverses the
polarity of the voltage applied to the cell stack 14, and begins
recharging the cell stack 14. The DC/DC converter 24 then resumes
standard operation according to either FIGS. 30 and 31 or FIGS. 32
and 33 as required by the new polarity presently commanded at the
battery terminals 55.
While the DC/DC converter 24 is executing under standard operation,
the processor 200 maintains a record of operation. Optionally, the
module controller 100 maintains a record of operation of each of
the DC/DC converters 24 and commands the desired operating modes of
each DC/DC converter 24 as a function of the duration of operation.
After a predetermined interval, the DC/DC converter 24 enters a
cell equalization routine. The cell equalization process is
required to prevent the formation of destructive zinc dendrites in
the cell stack 14.
According to one embodiment of the invention, a point system is
utilized to track operation of the DC/DC converter 24. Either the
DC/DC converter 24 or the module controller 100 monitors the
current flowing between the DC bus 28 and the cell stack 14 and
other operating conditions as a means of forecasting the health of
each particular cell stack 14 in the battery system 10. The current
and other monitored conditions are converted into an integer value,
or points. When the sum of these points reaches a user determined
maximum value, the DC/DC converter 24 is commanded to enter a
discharge only mode and begin the cell equalization process.
Monitored conditions may include, but are not limited to, factors
such as the total charge and discharge (amp hours) of the cell
stack 14, the rate of charge and discharge of the cell stack 14,
and the number of times the cell stack 14 has been cycled from a
charged condition to a discharged condition between strip cycles.
The module controller 100 may further limit the number of cell
stacks 14 entering an equalization routine at one time such that a
minimum storage capacity is maintained. Consequently, the number of
points accumulated by a DC/DC converter 24 may vary upon entering
the equalization routine. This number of points may be used to
determine the type of strip cycle and length of time the cell stack
14 will be in a strip cycle. By tracking cell stack 14 usage, only
those cell stacks 14 requiring equalization are commanded to enter
the equalization routine rather than conducting a strip of the
entire battery system 10, optimizing overall system availability.
Optionally, the DC/DC converter may be commanded to enter a strip
cycle based solely on the operating time. It is further
contemplated that still other methods of tracking duration of the
charging/discharging cycles in the cell stack 14 may be utilized
without deviating from the scope of the invention.
Referring next to FIG. 34, the steps in an improved equalization
routine 300 are illustrated. At step 302, the DC/DC converter 24
receives a command to enter the equalization routine. The command
may be generated internally as a function of monitoring operation
of the charge/discharge cycles of the connected cell stack 14.
Optionally, the command may be received from the module controller
100. The DC/DC converter 24 enters the discharge mode, for example,
by changing the set points for the hysteretic control. If the
discharge set point of the hysteretic control is set to a value
greater than the desired value of the voltage on the DC bus 28, the
DC/DC converter 24 begins discharging its respective cell stack 14
to the DC bus 28. Either a load present on the DC bus 28 or the
remaining cell stacks 14 draw the energy from the DC bus 28 to
maintain the desired voltage level on the DC bus 28. At step 306,
the equalization routine continues to loop back to the discharge
step 304 until the DC/DC converter 24 has discharged its respective
cell stack 14 and the voltage present on the battery has reached
zero volts. Upon reaching zero volts, the DC/DC converter 24
reverses the polarity present on the battery terminals 55, as shown
in step 308. The DC/DC converter 24 then begins charging the cell
stack 14 with the reversed polarity present at the battery
terminals 55. Because the equalization routine 300 is not concerned
with cell reversal, discharge of the cell stack 14 may continue at
a rapid rate down to zero volts rather than requiring discharge to
occur at continuously reduced steps of current.
Referring next to FIG. 35, discharge step 304, of the equalization
routine 300 is illustrated in more detail. During discharge, the
DC/DC converter 24 monitors the amplitude of the voltage present at
the cell stack 14, as shown in step 320. At step 322, the amplitude
of the voltage is compared against an initial threshold. If the
amplitude of the voltage is greater than the initial threshold, the
DC/DC converter 24 continues to regulate the current from the cell
stack 14 to the DC bus 28, discharging the cell stack 14, as shown
in step 324. If the amplitude of the voltage drops below the
initial threshold, the discharge routine checks if the amplitude of
the voltage has reached zero volts at step 326. While the amplitude
of the voltage remains below the initial threshold but greater than
zero volts, a high loss switching module is enabled, as shown in
step 328. When the amplitude of the voltage reaches zero volts, the
high loss switching module is disabled, as shown in step 330. Thus,
the DC/DC converter 24 is operable to automatically reverse the
polarity of the voltage present at the output terminals 260
connected to the cell stack 14 while maintaining the polarity on
the input terminals 210 connected to the DC bus 28 and while
continuously regulating the DC current in a bi-directional way.
This ability to reverse the polarity of the voltage at the cell
stack 14 accelerates cell equalization of the flow battery and
allows reverse charging of the flow battery module while
maintaining a common polarity as seen by the rest of the battery
system 10 at the input of the DC/DC converter 24.
Referring next to FIG. 36, the high loss switching module 350
controls the switching frequency of the modulation routine, as
shown in step 352, generating the gating signals 206, 208 of the
switching devices 230, 240 (see FIG. 29) to function as an "active
resistor". In contrast to traditional discharge methods, in which
resistors are connected across which energy may be dissipated, the
high loss switching module 350 causes energy to be dissipated in
the switching devices 230, 240. By increasing the switching
frequency of the modulation routine, the switching devices 230, 240
are turned on/off more frequently resulting in an increase in
losses associated with said switching. By waiting until the voltage
at the battery terminals 55 has dropped below an initial threshold,
the voltage and consequently the power across the switching devices
230, 240 is reduced. The current reference may also be reduced at
step 354, thereby further reducing the power dissipated across each
transition of the switching devices 230, 240.
As an additional advantage, the switching frequency may be linearly
varied between the normal operating frequency and an upper limit.
According to one embodiment of the invention, the switching
frequency may be increased between 4 and 16 times the original
switching frequency used by the DC/DC converter 24. In contrast,
traditional connection of resistors results in a single resistance
or a series of stepped resistances, resulting in finite steps of
current drawn from the cell stack 14 as it is discharged. Although,
shown in FIG. 36 as returning from block 358 to the discharge block
356, the high loss switching module 350 may be configured such that
it returns from block 358 to the change switching frequency block
352 and a continuously variable switching frequency may be
implemented. At step 356, the high loss switching module 350
operates at the selected switching frequency and current reference
to discharge the cell stack 14. The voltage level across the cell
stack 14 is monitored at step 358. When the voltage level across
the cell stack 14 has dropped below a lower, second threshold, one
or more of the switching devices may be latched on, generating a
short circuit to fully discharge the cell stack 14. The internal
resistance of the cell stack 14 limits the current under this short
circuit operating condition. By acting as an active resistance, the
high loss switching module 350 provides a method of equalizing the
cell with a resistive approach which is linearly variable across a
broad operating frequency in contrast to the typically fixed
passive resistive scheme. The DC/DC converter 24 has the capability
of strategically implementing the polarity reversal, the high loss
switching module 350, or both with full flexibility in range
settings of each.
Although the invention has been discussed with respect to the DC/DC
converter 24 illustrated in FIG. 29, it is further contemplated
that numerous other configurations of power converters may be
employed without deviating from the scope of the invention as long
as the power converter is configured to regulate bidirectional
current flow between the DC bus 212 and the output terminals 260
and to control the polarity of the voltage at the output terminals
260.
The following are further descriptions of the various attributes of
the components of the module 10 and for the operation of the module
10.
Module Electrolyte tanks 16--Complexed Bromine Storage, Control and
Level Management.
Design involves using three separate tanks 16 all connected at the
top for overflow protection. Tank levels are controlled through
pump speeds and differential head pressure due to the fluid height
in the tanks. Tanks are rotational molded with recessed areas for
pumps and plumbing.
Battery Cell and Flow Frame Design--gives Consistent Flow
Distribution under a very Wide Range of Fluid Parameters. Efficient
and Suitable for other Flow Battery Chemistries.
There are some approaches applied in the flow frame 34 plenum to
achieve 2P distribution (i.e., a two (2) parameter distribution
function) through successive bifurcations. A solution has been
designed that achieves even horizontal flow rates and sufficient
turbidity at each bifurcation to evenly distribute single or
multi-phase fluids.
Battery State-of-Charge Indicator
The 2P tank bottom pressure is logged using a submerged pressure
transducer. Referring to FIG. 28, as 2P builds during charge
(starts settling at .about.1 h, 100 A over 3 stacks) the pressure
increases as a linear function and therefore proportional to the
SOC. During discharge the 4 WV turns every 5-15 min and causes a 2P
build-up in the stacks with rapid 2P level drop-off.
Measuring battery SOC by measuring electrolyte pressure in an
electrolyte storage tank for a flow battery is the object of this
invention. To record a change in electrolyte density by logging
tank pressure is perhaps new, and can be accomplished through a
separate storage tank for the bromine phase in a zinc bromine flow
battery.
Module Electrolyte Flow Control for Maximum Efficiency, Long Term
Shut Down and De-Gassing Procedures
The module controller 100 is designed to control the flow system,
thermal management and protections, and monitoring all aspects of
the module. The module controller 100 monitors eight (8) cell
stacks to determine what mode the hardware should be in. For
example, if any one stack is discharging, the module will open the
2nd phase valve for discharge. The module controller also maintains
the battery temperature using a system of fans and heat exchangers.
Faults and system messages are also handled. For example, if the
module has a hardware fault, the controller takes the appropriate
action to safely shutdown the battery and to notify the system
controller of the fault. The module controller manages the
stripping function and all modes of operation.
A shut down procedure has been developed to rinse the bromine rich
second phase from the cell stacks so that the battery can be left
in a partially charged state indefinitely. The 2P tank plays an
integral role in this procedure as contains features that separate
the Bromine and aqueous phases, leaving the Bromine stored in the
2P tank for controlled dispatch. During the shutdown procedure, the
4-way valve 32 is rotated into the forward (top to bottom of stack)
position, the second phase valve is closed to minimize the amount
of bromine going to the cell stacks, the pumps 19 are operated at
reduced speed or pulsed to circulate electrolyte through the stacks
and purge the Bromine phase. The battery is then discharged to
remove any remaining reactive chemicals in the cell stack. Once the
battery reaches a safe voltage, the pumps are stopped and the
battery will be able to remain in this state indefinitely.
Module Thermal Management and Regulation using Specialty Heat
Exchangers 26
To prevent the electrolyte temperature from exceeding the allowable
operating range, the anolyte is directly cooled on the battery
module using an Air Cooled Heat Exchanger 26. To resist the
corrosive electrolyte the tube side of this heat exchanger is made
using a high purity Titanium material. The air side of this heat
exchanger uses Aluminum fins and ambient air is fan forced through
this exchanger to provide the cooling. This exchanger 26 is also
electrically isolated so that it floats at the electrolyte voltage
and there are no leakage currents that would accelerate
corrosion.
Dual (AC/DC) Power Supply
A single device utilized to provide control and/or aux power where
the source of the power is derived from redundant sources. Where
the power supply utilizes the high voltage regulated DC bus voltage
of a battery module output and/or PECC common DC Bus and the AC
source from the AC side of an inverter in the PECC system or
external AC source. Thus providing the capability of a fully
operational system with or without a connected AC source such as
the utility grid and where the primary/preferred source is
established as the DC input for the purpose of utilizing priority
renewable energy generation when possible, as it is connected to
the DC bus, and only utilizing the Grid source when not available.
The dual power supply remains completely seamless to the
control/aux output. The device is such that it may have multiple
source inputs for desired redundancy and provide one or more
outputs.
Use Common DC Bus 28 to Power Auxiliaries.
A single all inclusive device (Auxiliary Power & Control Module
(APC)) which provides multiple regulated & isolated DC voltages
for aux power of flow battery devices (pumps, controllers, fans,
heater etc) and controls, & inclusive of a complete DSP based
controls to all auxiliary equipments & instruments as well as
flow battery charging and discharging controls in a flow battery,
or in essence everything a flow battery requires to operate.
Additionally, the device includes external communication to provide
set up and control as well as complete monitoring of all aspects
both mechanical and electrical in the flow battery. The Device (Aux
Power & Control Module) shall be packaged on a single board
with mounting standoffs, power, i/o's & communication. And
where the device derives its source from a common regulated DC bus
at the output of the flow battery module or other energy storage
devices or sources that may be connected to the common dc bus, such
as the PECC common bus. Resulting in a self sustaining flow battery
module even in the event of an absent alternative generation
source. Significance is that all environmental and operational
functionality may be maintained as long as energy is stored and
available from the flow battery itself and not reliant upon any
external or indirect source to operate and control the flow
battery.
Method and Materials for Overmolding Battery Components
In the battery stack 14 the membranes, electrodes and Terminal
Electrodes (TE's) are insert molded into the their respective
"frames", i.e. the battery housing (these are generally referred to
as flow frames for membrane and electrode assemblies and endcaps
for TE assemblies). The electrode and frame plastics are modified
to improve the insert molding bond between these materials. Both
materials contain a high MFI polypropylene in the range of 60-120
gm/10 min at 230.degree. C., 2.16 kg. Both materials also contain a
polyolefin elastomer (ethyleneoctene copolymer). These additives
increase the mobility and miscibility of the plastics and result in
greater cohesion between the insert and the injected frame.
The inserts are also preheated to at least 200 deg F. immediately
prior to the insert molding process. This has a twofold purpose,
firstly it decreases the heat transfer required from the injected
plastic to melt the surface of the insert, thus increasing the time
in which both materials are in the molten state, therefore creating
a more intermixed and consistent bond. Secondly it reduces the
compression on the insert as the frame material shrinks after
molding. Reduced compression results in flatter and lower stressed
parts, which improves the cell gap and overall dimensional
consistency.
Manufacturing Techniques for Applying Activation Layers to the
Electrode Material
There are currently three techniques used to apply activation
layers to the electrode material. The first is used to apply a
granular activated carbon, the second and third processes are used
to apply carbon materials in sheet form (e.g. papers, felts, gas
diffusion layers). 1) Conductive glue is applied to the electrode
sheet using a porous roller. The sheet is then immediately immersed
in a fluidized bed of the granular activated carbon. This sheet is
then left to dry before pressing it under pressure and heat so that
the carbon granules are partially submerged in the electrode sheet.
This results in a permanent mechanical bond between the carbon and
the plastic sheet. 2) The carbon activation layer sheet is applied
to the electrode sheet during extrusion of the electrode in a
laminating process. Depending on the type of activation layer it
may or may not require a transfer sheet for stability during the
transfer process. 3) The activation layer is placed (or glued as
per process 1) on the electrode sheet and then pressed under
pressure and heat. As per process 1 this partially submerges the
activation layer into the electrode creating a mechanical bond.
Terminal Electrode 55 Manufacturing Procedure.
The terminal electrode is the current collecting point for the zinc
bromine battery. The current design uses a metal lug or busbar,
which is connected to a metal mesh material using either a
soldering or metal welding process. The metal mesh is imbedded into
a conductive carbon plastic sheet to form the terminal
electrode.
For the current production method, the Aluminum current collector
(comprising of an ultrasonically welded assembly of an expanded
mesh and bus bar) is placed in a compression mold along with sheets
of electrode material cut to fit the TE mold. This mold in then
heated under pressure using a Wabash press. The plastic then melts
and is formed into the desired TE shape. The mold is then cooled
under pressure, and the mold can be opened and the part removed.
The excess material (flash) is then removed. This part can be used
as an anode TE but must be coated with an activation layer if it is
to be a cathode TE.
Terminal Electrode 55 Manufacturing Process. Injection Molded
TE
A newly developed overmolding process has been developed to provide
a flat terminal electrode and to bond the overmolded flow frame
material to the conductive carbon plastic sheet of the terminal
electrode. A two-shot injection molding process and conductive
electrode material is developed to form a terminal electrode with
an overmolded end cap in a single mold. One factor in this
development effort is to achieve a carbon filled plastic material
with acceptable conductivity and the ability to be injection
molded. This can be achieved using ultra low molecular weight
plastic materials such as polypropylene waxes. The process results
in a molded, two-shot multi-component electrode/end cap.
For the multi-shot process, the Aluminum current collector is
inserted in an injection mold and the electrode material is
injection molded around it. This electrode material needs to be an
injection grade material with an MFI>1 gm/10 min at 230.degree.
C., 2.16 kg. Whilst the TE is still in the mold the frame material
is injected around it to make a complete endcap assembly. The
activation layer (for cathode endcaps) is then applied in a later
step via a heat and pressure process.
Battery Electrode 55 Material Formulation and Manufacturing
Process
The electrode for the V3 battery is an extrusion grade, carbon and
glass filled Polypropylene. The formulation is shown below in table
1.
TABLE-US-00001 TABLE 1 Formulation of electrode Material Percent
composition by weight Low MFI polypropylene 35-65% High MFI
polypropylene 5-15% Glass fiber 3-10% Carbon fiber 2-10% Graphite
5-15% Carbon black 7-20% Elastomer 2-10%
Where; MFI: Melt Flow Index in gm/10 min at 230.degree. C., 5 kg
The low MFI polypropylene (PP) has a MFI between 1 and 10 gm/10 min
at 230.degree. C., 2.16 kg. This material is required to achieve an
extrusion grade material and improves the dispersion of the carbon
fillers, which increases material conductivity. The high MFI
polypropylene (PP) has a MFI between 10 and 130 gm/10 min at
230.degree. C., 2.16 kg. This material is used to improve the
insert molding process. The glass fiber is required to improve
material stability and resistance to Bromine and thermal expansion.
Graphite is used for material stability and conductivity. Carbon
Black is used for conductivity and allows the electrode material to
achieve a bulk resistivity <2 .OMEGA.cm and a surface
resistivity <10 .OMEGA./cm.sup.2 Polyolefin elastomer is used
for improving the insert molding process. One more specific
formulation for the electrode 55 is shown below in table 2 where
the MFI is less than one.
TABLE-US-00002 TABLE 2 Formulation of electrode Material Percent
composition by weight Low MFI polypropylene 50% High MFI
polypropylene 10% Glass fiber 5% Carbon fiber 5% Graphite 10%
Carbon black 12% Elastomer 5%
The materials described above are not all required to be present in
the formulation but they illustrate a particular embodiment of the
formulation. Alternative components for battery electrode materials
include:
Carbon nanotubes, Carbon nanofibers, graphene, micro-graphites,
insert molding adhesion promoters, glass beads, talc, mica,
coupling agents, stabilizing fillers, crystallinity promoters and
anti-oxidants.
Battery Flow Frame 24 Material Formulation and Manufacturing
Process.
The frame material for the battery is an injection grade, glass
filled Polypropylene. The Formulation is as shown below in table 3
where the MFI is between about 25 and 50.
TABLE-US-00003 TABLE 3 Formulation of battery frame material
Material Percent composition by weight Polypropylene 65-90% Glass
fiber 5-15% Coupling Agent 0.5-7.0% Elastomer 3-15%
Where: The MFI (Melt Flow Index) of the final compound is between
12 and 50 gm/10 min at 230.degree. C., 2.16 kg The PP
(polypropylene) can be a single type or a blend to achieve the
final desired MFI. Glass Fiber is used to reduce the material
shrinkage. A coupling agent (Maleic Anhydride Modified
Polypropylene) is used for bonding the glass to polypropylene,
which improves the material strength, stability and Bromine
resistance. A polyolefin elastomer (ethyleneoctene copolymer) is
used for improving insert molding process. One more specific
formulation for the flow frame 24 is shown below in table 4 where
the MFI is about 40.
TABLE-US-00004 TABLE 4 Formulation of battery frame material
Material Percent composition by weight Polypropylene 70% Glass
fiber 15% Coupling Agent 5% Elastomer 10%
The materials described above are not all required to be present in
the formulation but they illustrate a particular embodiment of the
formulation. Alternative components for frame materials
include:
Insert molding adhesion promoters, glass beads, talc, mica,
coupling agents, stabilizing fillers, crystallinity promoters and
anti-oxidants.
It should be understood that the invention is not limited in its
application to the details of construction and arrangements of the
components set forth herein. The invention is capable of other
embodiments and of being practiced or carried out in various ways.
Variations and modifications of the foregoing are within the scope
of the present invention. It also being understood that the
invention disclosed and defined herein extends to all alternative
combinations of two or more of the individual features mentioned or
evident from the text and/or drawings. All of these different
combinations constitute various alternative aspects of the present
invention. The embodiments described herein explain the best modes
known for practicing the invention and will enable others skilled
in the art to utilize the invention.
* * * * *